1. Field of the Invention
The present invention pertains to a composite material flywheel device used for temporarily storing energy.
2. Description of the Related Art
The use of flywheel devices as apparatus for temporarily storing energy that is dissipated when transportation facilities, such as motor vehicles or railroad cars, are braked as well as nighttime surplus electric power that occurs in electric power systems is currently a subject under study.
While a large majority of flywheels of the flywheel devices are metallic ones, composite material flywheels made by molding a glass-fiber reinforced plastic, aramid fiber reinforced plastic or carbon-fiber reinforced plastic are also used to cater to the need for high-speed rotation.
A composite material flywheel is described in Japanese Unexamined Patent Publication No. 58-30545, for example, in which the flywheel is of such a construction that an outer part of a rotary shaft mounting portion 2 of a circular disk 1 made of an aluminum alloy thickens toward the outer periphery, a plurality of surfaces that are nearly vertical surfaces of the rotary shaft mounting portion 2 are made to have different inclinations from one another, a ring 4 molded of a high-strength carbon-fiber reinforced plastic is firmly fitted on a cylindrical portion 3 which is formed by the outermost part of the circular disk 1, and a plurality of radially directed slits 5 are provided in the circular disk 1 and ring 4, as shown in FIGS. 6 and 7.
Also, a flywheel intended for storing energy is described in U.S. Pat. No. 4,569,114, for example, in which the flywheel is of a construction comprising a metallic hub 8 having a plurality of spokes 6 and a ring 7 which are one-piece molded, a glass-fiber reinforced plastic inner ring 9 provided on an outer surface of the metallic hub 8 and a carbon-fiber reinforced plastic outer ring 10 provided on an outer surface of the glass-fiber reinforced plastic inner ring 9, as shown in FIG. 8.
With the composite material flywheel in which a high-strength carbon-fiber reinforced plastic ring is firmly fitted on a cylindrical portion of a circular disk and a plurality of radially directed slits are provided in the circular disk and a ring, the ring could oscillate in its axial direction due to bending of the circular disk during high-speed rotation, making it difficult to maintain delicate geometric relationship with surrounding equipment.
Although the composite material flywheel molded of a high-strength carbon-fiber reinforced plastic allows operation at such a high rotating speed that is not achieved with glass-fiber reinforced flywheels or aramid fiber reinforced flywheels, high degrees of stress and strain occur in the interior of the flywheel and the inside diameters of the metallic circular disk and hub increase due to expansion caused by a centrifugal effect, thus creating a gap between the flywheel and its shaft. This could cause such problems as whirling or other instability-related phenomena.
Furthermore, because the ring of the metallic hub is formed of the same metal as the spokes in the aforementioned energy storage flywheel, there arises a problem related to the strength of the ring and there exist limitations in increasing the rotating speed.